JPH11163390A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high optical coupling efficiency between a light beam receiving element and a light beam outputting element by arranging a light beam outputting element, a light beam receiving element and an optical path changing means on the main surface of a substrate, and forming a light-reflecting film on a region irradiated with a part of the outputted light beam. SOLUTION: A light-receiving element 10 and a laser diode 50 are laminated on a retaining substrate 1, constituted of a silicon substrate 1a and an SiO2 film 1b of a main surface. An incident end surface 11 of the element 10 and a high reflecting end surface 51 of the diode 50 are made to face each other, and a light-reflecting film 60 composed of Au is formed on a region between the surface 11 and the surface 51. A part of the outputted laser light enters directly a slant face 11a, and a part is reflected by the reflecting film 60 and enters the slant face 11a. It acts as an optical path change means which changes traveling direction of the laser light. By suitably adjusting a light-receiving diode D1 , a greater part of the laser light from the diode 50 is made to reach the light-receiving diode D1 , so that the optical coupling efficiency between the diode 50 and the element 10 can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector, and more particularly to a photodetector suitable for a light-receiving element for monitoring an output of a semiconductor laser module used in an optical communication system.

A semiconductor laser module has a built-in light receiving element for monitoring an optical output in order to compensate for the temperature characteristics of a laser diode. The light receiving element receives the laser light output from the laser diode and converts it into a photocurrent. This photocurrent is input to the feedback circuit and fed back to the laser diode. In order to simplify the feedback circuit and improve the performance of the feedback control, it is preferable to generate a larger photocurrent.

[0003]

2. Description of the Related Art Conventionally, a photodiode having an edge incident structure has been used as a photodetector for monitoring the output of a laser diode. The photodiode having the edge incidence structure is arranged so that an incident end face on which light to be detected is incident is opposed to a high reflection end face of the laser diode. Laser light emitted from the highly reflective end face of the laser diode enters the light receiving region from the incident end face of the photodiode. The photodiode generates a photocurrent according to the intensity of the laser light incident on the light receiving region. By observing this photocurrent, the optical output of the laser diode can be monitored.

[0004]

The light receiving area of a photodiode having an edge incident structure is usually a thin layer having a thickness of about 2 to 3 μm. On the other hand, the laser light emitted from the high reflection end face of the laser diode has a spread of about 30 ° in the normal direction of the active layer. Therefore, of the laser light emitted from the high reflection end face of the laser diode, a small amount of light is incident on the light receiving region of the photodiode.
In other words, when the laser diode and the photodiode having the edge incidence structure are optically coupled, it is difficult to obtain a large coupling efficiency.

It is an object of the present invention to provide a photodetector capable of improving the efficiency of light coupling with a light beam emitting element.

[0006]

According to one aspect of the present invention, there is provided a substrate having a main surface, and an emission end surface mounted on the main surface of the substrate and emitting a light beam. A light beam emitting element arranged so that a part of the light beam irradiates a partial area of the main surface of the substrate, and a light receiving unit that is mounted on the main surface of the substrate and detects an incident light beam. A light receiving element, including a light beam emitted from the light beam emitting element, an optical path changing means for changing a traveling direction of the light beam so as to be incident on a light receiving portion of the light receiving element, and a main surface of the substrate, A light reflecting film formed on a light beam irradiation area irradiated by a part of the light beam emitted from the light emitting end face of the light beam emitting element, and reflecting the light beam and making the light beam incident on the light path changing means; Module Le is provided.

By arranging the optical path changing means, the light path of the light beam can be converted so that the light receiving element can easily receive the light. Further, by disposing the light reflecting film, a light beam that does not directly enter the optical path changing means can be reflected and entered. Thus, the optical coupling efficiency between the light beam emitting element and the light receiving element can be increased.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described by taking a semiconductor laser module having a laser diode and a light receiving element for monitoring its output as an example.

FIG. 1 is a sectional view of a photodetector according to an embodiment of the present invention. The photodetector according to the embodiment includes a silicon substrate 1a and a SiO ₂ film 1b formed on a main surface thereof.
And a laser diode 50 disposed on the main surface of the support substrate 1 having a laminated structure of The light receiving element 10 and the laser diode 50 are arranged such that the incident end face 11 of the light receiving element 10 and the high reflection end face 51 of the laser diode 50 face each other.

The laser diode 50 includes an active layer 53, an n-type cladding layer 54 sandwiching the active layer 53 from above and below, and a p-type cladding layer 55. Laser diode 50
The high-reflection end face 51 and the low-reflection end face 52 constitute an optical resonator. The low-reflection end face 52 and the high-reflection end face 51 are coated with low-reflection and high-reflection coatings, for example, so that the reflectances are 30% and 80%, respectively. The laser light pumped into the optical resonator is emitted from the low reflection end face 52 to the outside and also slightly emitted from the high reflection end face 51.

The active layer 53 of the laser diode 50 is arranged substantially parallel to the main surface of the support substrate 1. For this reason,
The optical axis of the laser light emitted from the high reflection end face 51 of the laser diode 50 is substantially parallel to the main surface of the support substrate 1.

The light receiving element 10 includes a light receiving element substrate 12 made of n-type InP and a light receiving diode formed on an upper main surface thereof. The lower main surface of the light receiving element substrate 12 is fused to the main surface of the support substrate 1 via the fusion layer 18.

On the upper main surface of the light receiving element substrate 12, an n-type InP layer 13, a non-doped InGaAs layer 14, and an n ^- type InP layer 15 are laminated. These layers are formed by, for example, chloride vapor phase epitaxy (chloride VPE) using solid In and Ga as group III materials and PH ₃ and AsH ₃ as group V materials. In chloride VPE, In and Ga react with Cl ₂ gas and are supplied onto the substrate.

The p-type regions 15a and 15b are formed by thermally diffusing Zn, which is a p-type impurity, in a part of the n ⁻ -type InP layer 15. Electrodes 16a and 16b are formed on p-type regions 15a and 15b, respectively.

The p-type region 15a of the InP layer 15 is
InGaAs layer 14 and n-type InP layer 13
Light receiving diode D having a pin structure₁Is formed, and In
P-type region 15b of P layer 15, non-doped InGaAs
The layer 14 and the n-type InP layer 13 drive the pin structure.
Dynamic diode D_TwoIs configured. Photodiode D
₁Is formed in the light receiving portion of the light receiving element 10.
Hit.

A ridge portion where the incident end face 11 of the light receiving element 10 and the lower main surface of the light receiving element substrate 12 intersect is chamfered, and an inclined surface 11a inclined with respect to the main surface of the support substrate 1 is formed. . Lower main surface and slope 1 of light receiving element substrate 12
1a is non-reflective coated with, for example, a SiN film 17. The angle between the slope 11a and the main surface of the support substrate 1 is defined as θ.

Of the main surface of the support substrate 1, the highly reflective end face 51 of the laser diode 50 and the incident end face 1 of the light receiving element 10
The light reflection film 60 is formed on the area between the light reflection films 1 and 2.
The light reflection film 60 is formed of, for example, Au.

The laser light emitted from the high reflection end face 51 of the laser diode 50 has a divergence angle of about 30 ° in the vertical direction. A part of the emitted laser light is directly incident on the slope 11a, and another part is reflected by the light reflection film 60 and is incident on the slope 11a. The laser light incident on the slopes 11a is refracted according to the refractive index difference between InP and the atmosphere to reach the area where the light-receiving diode D ₁ is formed. That is, the slope 11a functions as an optical path changing unit that changes the traveling direction of the laser light.

By appropriately adjusting the position at which the light receiving diode D ₁ is disposed and the angle θ, most of the laser light emitted from the high reflection end face 51 of the laser diode 50 can reach the light receiving diode D _1. . For example,
Is set in the range of 45 to 60 °. Moreover, since forming the light reflecting film 60 on the main surface of the supporting substrate 1, is incident on the inclined surface 11a is also a laser beam for irradiating a main surface of the supporting substrate 1, it is possible to reach the receiving diode D ₁ . Thus, the optical coupling efficiency between the laser diode 50 and the light receiving element 10 can be increased.

FIG. 2 shows an equivalent circuit of the light receiving element 10.
Between the electrodes 16a and 16b, a light receiving diode D ₁ and the drive diode D ₂ are connected in series with opposite polarity to each other. Electrode 16a corresponds to the anode of the light-receiving diode D _1, the electrode 16b corresponds to the anode of the drive diode D _2.

The electrode 16a is grounded via a resistance element R, and a voltage generated across the resistance element R is taken out as an output signal. To drive the diode D _2, a forward bias is applied from the DC power source E. Receiving diode D ₁ is reverse biased and conducts in response to incident light.

P-type region 1 corresponding to drive diode D ₂
5b is, p-type region 15a corresponding to the receiving diode D ₁
It has a substantially larger area and can supply a larger drive current. Further, while the junction capacitance C _p of the drive diode D ₂ is large, the junction capacitance of the photodiode D ₁ is small. Therefore, the light receiving diode D ₁ shows a fast response to incident light.

For example, the laser diode 50 shown in FIG.
The intensity of the laser light emitted from the high reflection end face 51 is about 2 m
At W, a photocurrent of about 0.45 mA could be detected. On the other hand, when the light reflection film 60 was not formed, only a photocurrent of about 0.3 mA could be detected.
By forming the light reflection film 60, the magnitude of the photocurrent could be increased to about 1.5 times.

According to the above embodiment, since the photocurrent can be increased, it is possible to simplify the feedback circuit and to achieve high performance of the feedback control.

Next, a method of manufacturing the photodetector shown in FIG. 1 will be described with reference to FIG. FIG. 3 is a cross-sectional view of the substrate before separation into individual chip units. An n-type InP layer 13 and a non-doped InGaAs are formed on the upper main surface of the light-receiving element substrate 12 made of n-type InP with the (100) plane exposed.
The layer 14 and the n ⁻ -type InP layer 15 are
Deposited by PE. In the InP layer 15, Zn is thermally diffused into regions corresponding to the p-type regions 15a and 15b in FIG. 1 to form p-type regions 15a and 15b.

An electrode layer is deposited and patterned on the InP layer 15 to form electrodes 16a and 16b. Electrode 1
6a and 16b are formed of, for example, a material Au.

The lower main surface of the light receiving element substrate 12 is covered with a mask pattern so as to expose a region corresponding to the end face of the light receiving element 10 of FIG. 1 and its vicinity, and the light receiving element substrate 12 is partially etched. A groove 20 is formed. When hydrochloric acid or a mixed solution of Br, HBr and H ₂ O is used as an etchant, a (111) plane or a crystal plane in the vicinity thereof appears on the side surface of the groove 20. This side surface corresponds to the slope 11a shown in FIG. At this time, the angle θ between the imaginary plane extending the lower main surface of the light receiving element substrate 12 toward the opening of the groove 20 and the side surface of the groove 20 is about 55 °. As an etchant, a mixed solution of HCl and H ₃ PO ₄ or B
Ethanol containing r can also be used.

After forming the groove 20, the antireflection film 1 is formed so as to cover the side surface of the groove 20 and the lower main surface of the light receiving element substrate 12.
7 is formed. The antireflection film 17 has a thickness of, for example, 0.2 μm.
m SiN film.

On the surface of the antireflection film 17, a flux layer 18 is formed on a region other than the side surface of the groove 20. Flux layer 18
Are, for example, a 0.1 μm thick Ti layer, a 0.1 μm thick Au layer, a 2 μm thick Sn layer, and a 0.1 μm thick A layer.
It has a four-layer structure in which u layers are stacked in this order.

The substrate shown in FIG. 3 is cleaved along the groove 20.
Separate into individual chip units. The fusion layer 18 is fused onto the main surface of the support substrate 1 shown in FIG.
Is fixed to the support substrate 1. At this time, by forming the alignment marks 4 on the main surface of the support substrate 1, highly accurate alignment can be performed.

FIG. 4 is a schematic sectional view of a photodetector according to a modification of the above embodiment. Of the main surface of the support substrate 1,
High reflection end face 51 of laser diode 50 and light receiving element 10
A shallow concave portion 3 is formed in a region between the incident end face 11 and the light incident end face 11. The side surface of the concave portion 3 is a gentle slope or an oblique curved surface. The recess 3 is formed by, for example, wet etching using KOH. The inner surface of the recess 3 is covered with the light reflecting film 60. Other configurations are the same as those of the embodiment shown in FIG.

By forming the inner surface of the concave portion 3 into an appropriate shape, for example, a shape such that the (111) plane is exposed on the slope, more laser light can reach the light receiving diode D ₁ of the light receiving element 10. I can do it.

FIG. 5 is a schematic perspective view of a semiconductor laser module using the photodetector according to the above embodiment. A recess 71 having a flat bottom surface is formed on the upper surface of the ceramic package 70, and the support substrate 1 is fixed on the bottom surface of the recess 71. On the main surface of the support substrate 1, the laser diode 50 and the light receiving element 10 shown in FIG. 1 are fixed.
A light reflection film 60 is formed on a region between the light receiving element 10 and the laser diode 50 on the main surface of the support substrate 1.

The tip of the optical fiber 72 faces the low reflection end face 52 of the laser diode 50,
And the optical fiber 72 are optically coupled. Optical fiber 72
The portion where the core wire near the front end is exposed is positioned by a V groove 73 formed on the main surface of the support substrate 1. V
The groove 71 is formed by, for example, etching a (100) plane silicon substrate using KOH as an etchant using an SiO ₂ pattern as a mask. At this time, the (111) plane is exposed on the side surface of the V groove 71.

The optical fiber 7 on the main surface of the support substrate 1
A groove 74 extending in a direction perpendicular to the optical axis of the optical fiber is formed in a region between the tip of the optical fiber 2 and the low reflection end face 52 of the laser diode 50 by, for example, dicing.
The groove 74 serves to prevent the resin from flowing when the tip of the optical fiber 72 is fixed with the resin, for example.

Laser light emitted from the low reflection end face 52 of the laser diode 50 enters the optical fiber from the end face of the optical fiber 72 and propagates through the optical fiber 72. The laser beam emitted from the high reflection end face of the laser diode 50 is detected by the light receiving element 10 and the laser diode 5 is detected.
The output of 0 can be constantly monitored.

In the above embodiment, the case where the laser beam emitted from the laser diode is detected has been described. However, the present invention is not limited to the laser diode, but can be applied to the case where the light beam emitted from the blockage of the light beam is detected. For example, it is possible to detect a light beam emitted from the emission end face of the optical fiber.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0039]

As described above, according to the present invention,
Many components of the light beam emitted from the light beam emitting element can reach the light receiving portion of the light receiving element. For this reason, the light beam intensity can be efficiently observed by the light receiving element.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a photodetector according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a light receiving element of the photodetector shown in FIG.

FIG. 3 is a cross-sectional view of a substrate for describing a method for manufacturing a photodetector according to an embodiment.

FIG. 4 is a schematic sectional view of a light detection device according to a modification of the embodiment.

FIG. 5 is a perspective view of a semiconductor laser module to which the photodetector according to the embodiment is applied.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 support substrate 1a silicon substrate 1b SiO ₂ film 3 concave portion 4 alignment mark 10 light receiving element 11 incident end face 11a slope 12 light receiving element substrate 13 n-type InP layer 14 undoped InGaAs layer 15 InP layer 15a, 15b p-type region 16a, 16b Electrode 17 Antireflection film 18 Flux layer 20 Groove 50 Laser diode 51 High reflection end face 52 Low reflection end face 53 Active layer 54, 55 Cladding layer 60 Light reflection film 70 Ceramic package 71 Depression 72 Optical fiber 73 V groove 74 Groove

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroki Murakami 1000, Azagami, Azagami-cho, Showa-cho, Nakakoma-gun, Yamanashi Inside Fujitsu Quantum Devices Co., Ltd. No. 1 Inside Fujitsu Limited

Claims (6)

[Claims] A substrate having a main surface; and an emission end face mounted on the main surface of the substrate and emitting a light beam, wherein a part of the light beam emitted from the emission end face is formed on a main surface of the substrate. A light beam emitting element arranged to irradiate a partial region; a light receiving element mounted on a main surface of the substrate and including a light receiving unit for detecting an incident light beam; and emitting light from the light beam emitting element. Optical path changing means for receiving the light beam and changing the traveling direction of the light beam so as to be incident on a light receiving portion of the light receiving element; and light emitted from the emission end face of the light beam emission element on the main surface of the substrate. A light reflecting film formed on a light beam irradiation area irradiated by a part of the beam, the light reflecting film reflecting the light beam and making the light beam enter the optical path changing means. 2. The optical module according to claim 1, further comprising a concave portion formed in the light beam irradiation region on the main surface of the substrate, wherein the light reflecting film covers an inner surface of the concave portion. 3. An optical axis of a light beam emitted from the light beam emitting element is parallel to a main surface of the substrate, and the emitted light beam spreads at an angle, and a part of the emitted light beam is in the light irradiation area of the substrate. 3. The optical module according to claim 1, wherein the optical path conversion unit is configured to include a slope that is obliquely arranged with respect to a main surface of the substrate. 4. 4. The light-receiving element has a light-receiving element substrate defined by first and second main surfaces facing each other and an incident end surface, wherein the first main surface is formed of the substrate. 4. The light-receiving unit according to claim 3, wherein the light-receiving unit is disposed on the second main surface side of the light-receiving element substrate, wherein the light-receiving unit is disposed so as to face the main surface, the incident end face is opposed to the light-emitting end surface of the light beam emitting element. An optical module as described. 5. The optical module according to claim 4, wherein the optical path changing means includes a slope defined on the incident end face of the light receiving element substrate. 6. The light reflection film is formed on an area between the emission end face of the light beam emission element and the incidence end face of the light receiving element substrate on a main surface of the substrate. Or the optical module according to 5.